There are numerous processes and transfer situations where a material must be transferred between zones having different fluids and/or the same or different pressures without a significant mixing of the fluids or communication of the different zones. An example of such a situation is a material being placed in a chute or hopper at atmospheric pressure in the presence of air and being transferred into a processing unit or system having a different gaseous atmosphere or pressure above or below atmospheric. A specific sitution is found in the tobacco industry where it is desirable to transfer a quantity of pliable cut tobacco filler at atmospheric pressure from a chute into a closed processing system which contains a gaseous processing fluid at a pressure above atmospheric pressure without the introduction of significant quantities of air.
One type of device commonly used for this purpose is a so-called rotary valve or rotary feeder. Generally, a rotary feeder includes a housing carrying a rotary element which has a member of pockets that rotate successively past an inlet opening in the housing through which materials can be introduced into the pockets. The pockets then rotate past a discharge outlet where the materials exit the feeder. The rotor is sealed around the inlet and, thus, the different pressures and atmospheres existing between the inlet and the outlet of the rotary valve are maintained. Although these rotary feeders give satisfactory service with some materials and under certain conditions, there are a number of situations where the materials are abrasive so that the interface between the rotor and the inlet seal becomes worn and the seal is destroyed in a relatively short time.
Another type of valve for use in similar situations uses elastic elements. For example, the valve can have two or more inflatable diaphragms which are normally deflated to permit material to pass and inflated to a sealing engagement with a co-acting valve seat member. Another elastic element valve uses a tubular diaphragm which is pinched closed to stop the passage of the material.
The pinched type diaphragm is subjected to relatively quick deterioration of the elastic element, in that, it is bent and pinched into distortion and highly stressed conditions on each operation. The inflatable diaphragm valves are not suitable in situations where there is high pressure on one side of the valve so that, when it is opened, a flow is created into the low pressure area of the valve. Thus, if the material is passed through the valve from the low to a high pressure zone, it must flow counter to the back flow of fluid and is subject to high turbulence, a loss of flow rate, and other detrimental effects.
One inflatable sealing valve has been developed to overcome the pressure problem by using a three-tiered inflatable diaphragm structure having two zones through which the material must pass to equalize the pressure between zones. Such a valve is illustrated in U.S. Pat. No. 3,491,922. The primary drawback to this valve is its complexity and its inability to substantially eliminate the admixing of the fluids in the different zones.